Molded EPS is a closed cell light-weight foam plastic formed of Styrenic Hydrocarbon. It is manufactured by placing polystyrene beads, containing a blowing agent, into a mold and exposing them to heat. The heat causes the blowing agent to expand the beads, which fuse together to form a large block from which packaging members are cut. As an alternative, the mold may be in accordance with the packaging element configuration. The molded material is measured in terms of pounds per cubic foot density (pcf).
The mechanical properties of molded EPS depend largely upon density in general, with strength characteristics increasing with density. However, such variables such as the grade of raw material used, geometry of the molded part and processing conditions will affect packaging properties and performance. It is to be understood that variables inherent to any test specimen may result in properties varying .+-.10-15% from listed values.
Molded EPS is an effective, economical packaging medium for foodstuffs, pharmaceuticals and other perishables which must be shipped and stored under thermally controlled environments. EPS is highly resistant to heat flow, with its uniform, closed cellular structure limiting radiant, convective and conductive heat transfer. The thermal conductivity (k factor) of molded EPS is known to vary with density and exposure temperature.
The cellular structure of molded EPS is essentially impermeable to water and provides zero capillarity. However, due to the fine interstitial channels within the bead-like structure, moisture may be absorbed under total immersion. Although molded EPS is relatively impermeable to liquid water, it is moderately permeable to vapors under pressure differentials. Vapor permeability is a function of both density and thickness. However, generally speaking, neither water nor water vapor affects the mechanical properties of EPS.
Molded EPS is an inert, organic material. It provides no nutritive value to plants, animals or micro-organisms. It will not rot, and is highly resistant to mildew.
Molded EPS is unaffected by water and aqueous solutions of salts, acids and alkalis. Most organic solvents are not compatible with molded EPS and this must be considered when selecting adhesives, labels and coatings for direct application thereto.
As stated above, this invention relates to standard molded EPS which at room temperature is compressed at different ranges of deflection in varying duration and/or dimension to provide an enhanced packaging product .